1. Field of the Invention
The present invention relates to a method of forming a textile, and more particularly, to a method of forming a textile having therein an undulating wire member which exhibits shape memory behavior.
2. Brief Description of the Prior Art
Vascular graft techniques have been known for approximately 30 years. Knitted or woven tubes are formed from fibrous materials and are employed to repair a damaged body tube, such as a damaged vascular structure. Patients with diseased or damaged vascular structures, or other body tubes, can be successfully treated with such graft structures. For example, a patient with an abdominal aortic aneurysm can have the aneurysm repaired with a suitable graft. However, pure graft structures, although designed to enhance fluid integrity of the damaged body tube, do not have the capability to support themselves or to be secured in place. Thus, invasive surgery is required to attach the structures to the damaged vascular area, which may result in a long, expensive hospital stay and attendant dangers due to the major surgery required.
In an effort to overcome the problems with graft structures, an alternative approached was developed in the early 1980s. So-called stents were developed which could expand a clogged artery, for example, and be self-securing by virtue of an interference fit with the artery wall. Such structures might be self-expanding, by virtue of recovery of elastic stress, or might be formed of ductile materials and expanded with a balloon catheter. However, so-called stent structures do not in themselves enhance the fluid integrity of the body tube. They rely on the diseased wall of the body tube to maintain fluid integrity, and are directed primarily to expanding the body tube such as, for example, a clogged artery.
Recently, devices have been developed which combine the benefits of both graft and stent structures. In these types of devices, a stent structure is secured to a graft structure. The graft structure serves to enhance fluid integrity of the body tube, while the stent structure helps to support the graft and to secure the graft in place against the body tube. These types of devices can be implanted with a catheter procedure, and thus do not require invasive surgery.
U.S. Pat. No. 4,130,904 to Whalen, U.S. Pat. No. 4,313,231 to Koyamada, U.S. Pat. No. 5,507,767 to Maeda et al., U.S. Pat. No. 5,591,195 to Thaeri et al., U.S. Pat. No. 5,667,523 to Bynon et al., and U.S. Pat. No. 5,674,277 to Freitag all disclose combined stent/graft structures. Although these structures have significantly enhanced patient treatment, a number of problems still remain. Heretofore, most combined stent/graft structures have fastened the stent to the graft via suturing or glue. These methods are problematic. Suturing may not be repeatable for quality control, can be unreliable, resulting in potential loosening of the stent from the graft, with catastrophic results for the patient, and may degrade fluid integrity of the graft due to the needle holes required for the suturing. Gluing may also be unreliable and may pose repeatability and quality control problems as well. U.S. Pat. Nos. 5,571,173 and 5,578,071, both to Parodi, show a graft structure with an undulating wire which is woven into the graft. The wire is confined to an end of the graft structure, and is made of a ductile material. It must be expanded by a balloon catheterization procedure. The Parodi patents suggest that the stent can be woven into the interior of the graft, but provide no details as to how this can be accomplished. Further, the undulating wire of Parodi appears to have a global axis which is parallel to the fill yarns of the graft, and thus, could not be extended over the whole length of the graft structure.
In view of the deficiencies of prior art devices, it would be desirable to provide a stent/graft structure wherein the stent is integrally secured to the graft in a manner which does not compromise fluid integrity, is reliable, and is repeatable for quality control purposes. It would also be desirable if the stent member in the combined structure is secured in a way which lent itself to easy manufacturing. Yet further, it would be desirable if a global axis of the stent member could describe a generally helical path with respect to the graft structure, such that a single stent member could extend substantially over the whole length of the graft, thus providing support throughout the length of the graft.